1. Field of the Invention
The present invention relates to a thin film transistor and the manufacturing method thereof, and more particularly to a thin film transistor used in a thin film transistor liquid crystal display.
2. Description of the Related Art
In an active matrix liquid crystal displays, a thin film transistor (TFT) is commonly adopted for good driving and switching capabilities. FIG. 1 shows the essential components of a TFT used in a thin film transistor liquid crystal display (TFT-LCD). The substrate 1 is made from glass or quartz. A metal layer 2a is used as the gate electrode of the TFT. The electrode 2b is an electrode of a storage capacitor. A insulating layer 3 is formed on the substrate 1. A semiconductor layer 4 is further formed above the insulating layer 3 and usually made from amorphous silicon. An n type doped polysilicon layer 5 and a metal electrode 6 are used to form source/drain electrodes of the TFT. A passivation layer 7 is formed above the substrate 1. A transparent conductive layer 8, such as an ITO layer, is used to form the pixel electrode. Between the source electrode and the drain electrode, a channel 9 is defined.
According to the TFT shown in FIG. 1, the amorphous silicon layer 4 is formed on the insulating layer 3, and the channel 9 is defined by etching the amorphous silicon layer 4. During the above etching process, if any amorphous silicon is left above the insulating layer 3 at the position outside the TFT, it will harm the properties of the TFT and reduce the quality of the TFT-LCD. Additionally, two dielectric layers, including the insulating layer 3 and the passivaton layer 7, are formed on the substrate 1 and will reduce the transmittance of the substrate 1.